Incidence of first-degree perineal laceration
Eleven trials involving 3618 women were included in this outcome, 3581 women contributed data. The result of meta-analysis indicated that women in lubricant group had no statistically difference in the incidence of first-degree perineal laceration when compared with those in standard care group (RR 1.18, 95%CI 0.92 to 1.52; I2=87%; very low certainty due to serious risk of bias, serious inconsistency and serious imprecision) (Table 1, Figure S11).
Subgroup analyses showed that there was significant subgroup effect between parity groups (P interaction<0.001) (Figure 12), but not between lubricants type groups and between overall risk of bias (Pinteraction=0.66 and Pinteraction=0.58, respectively) (Figure S13, Figure S14). The heterogeneity of multiparous women groups, obstetric gel groups and high risk of bias groups was significantly reduced after subgroup analysis (I2=0%, I2=48% and I2=20%, respectively), while significant heterogeneity remained within nulliparous women groups, liquid wax groups and low high risk of bias groups (I2=82%, I2=92% and I2=90%, respectively). This heterogeneity might partially result from studies of nulliparous women, liquid wax and low risk of bias (Figure S13, Figure S14).
The result analyzed based on parity indicated that both multiparous and nulliparous women in lubricant group had statistically difference in the incidence of first-degree perineal trauma when compared with those in standard care group. Multiparous women had a lower incidence of first-degree perineal trauma (RR 0.69, 95%CI 0.59 to 0.80; I2=0%) (Figure S12), while nulliparous women had a higher incidence of first-degree perineal trauma (RR 1.38, 95%CI 1.03 to 1.86; I2=82%) (Figure S12), which might be associated with decreasing for incidence of second-degree perineal laceration and the incidence of first-degree perineal trauma was increasing relatively. Therefore, it was uncertain whether lubricant increased or reduced the incidence of first-degree perineal trauma for nulliparous women.